The present invention is directed to heat sinks primarily for use in dissipating waste heat generated by electronics such as power modules, transistors, microprocessor components and assemblies, and especially computer chips. These heat sinks, comprising a planar base and upright fins, provide high heat transfer from concentrated heat sources using a cooling fluid flowing through the heat sink under laminar flow conditions. The fins are located on one side of the base plate and are arranged in columns and rows that define parallel channels for fluid flow.
Research activities have focused on developing heat sinks to efficiently dissipate heat from highly concentrated heat sources such as microprocessors and computer chips. These heat sources typically have power densities in the range of 4 to 10 watts per square centimeter (3.5 to 9 Btu per second per square foot) and relatively small available space for placement of fans, heat exchangers, heat sinks and the like.
The typical liquid-cooled heat sinks have a fin density in the range of 2 to 7 fins per centimeter (6 to 18 fins per inch) and a fin height in the range of 2 to 5 millimeters (0.08 to 0.2 inch). Typical air-cooled heat sinks, on the other hand, have a fin density of about 3 to 10 fins per centimeter (8 to 25 fins per inch) and a fin height of about 10 to 15 millimeters (0.4 to 0.6 inch). Also fin thickness of 0.05 to 0.25 mm (0.002 to 0.01 inch) is common depending on the fin material.
Existing liquid-cooled heat sinks used for these purposes have generally used a high heat capacity-rate fluid such as water or water-glycol solution to transfer heat from the electronic heat source to the cooling fluid stream typically air. A typical liquid-cooled heat sink for electronics consists of a copper block with drilled circular passages for liquid flow that are connected in a serpentine pattern by means of hairpin tubes. The electronic heat source is bonded to one face of the block and cooling liquid flows through the drilled circular passages. Heat sinks of this type have also used a serpentine tube mounted on one side of a plate with the electronic heat source bonded on the other side of the plate. These types of heat sinks provide low heat transfer rate due to the wide spacing of the serpentine flow passages. Also, they tend to be heavy.
Existing air-cooled heat sinks used for these purposes comprise an array of parallel fins on one side of a plate. The electronic heat source is bonded to the opposite side of the plate. The parallel fins bonded to the plate form channels with relatively large aspect ratio of the channel width to channel height. Cooling air is drawn through the fins by means of a fan generally placed over the fins. The cooling capacity of such heat sinks tends to be low due to low heat capacity of air.
In conventional electronics cooling heat exchangers, turbulent flow with high flow velocity is necessary in order to achieve good heat transfer. This results in high pumping power for the cooling fluid. In addition, the high velocity turbulent flow contributes to the noise level of the electronic device, which is not desirable. Motivated by these considerations, a low velocity laminar flow is employed in the present invention so as to lower the pumping power and to reduce the noise associated with high velocity turbulent flow.
The present invention is directed to liquid-cooled or air-cooled metallic heat sinks such as those made of aluminum or aluminum-based alloys and copper or copper-based alloys. These heat sinks are capable of dissipating heat generated by concentrated heat sources using relatively low velocity larninar flow of the cooling fluid. The heat sinks are formed as a singular structure by casting, pressing, extruding, forging or by machining operations like electron discharge machining (EDM) and milling. As formed, the present heat sink comprises a planar base with integrated vertical fins on one side. The fins are arranged so that they cover the base to form parallel arrays across its width. The parallel fin arrays extend in a serial fashion along the flow length of the base with intervening gaps between successive arrays.